1. Field of the Invention
The present invention relates to a router network, having a saving function, for a subordinate LAN (Local Area Network) at a router fault.
2. Related Arts
As a consequence of the recent drastic expansion of the Internet, companies have begun to establish LANs, which employ the local-area Ethernet protocol, for connecting pluralities of personal computers, and have also begun to use routers to interconnect pluralities of LANs and build Intranets.
Commonly employed, for example, are the network configurations shown in FIGS. 52 and 53, wherein segments are allocated for individual organizations and are connected together by a router. In the networks in FIGS. 52 and 53, LAN-I, LAN-II and LAN-III constitute segments, and transmissions must pass through routers A, B and C in order for communication via LAN-IV (FIG. 52), or an ATM switch (FIG. 53), to take place between the segments and the terminals DTE-A, DTE-B and DTE-C of other segments.
When one of the routers A, B and C malfunctions, communication with the other segments may be disabled. To resolve this problem, as is shown in FIGS. 54 and 55, an Intranet, in which two IP routers B and Bxe2x80x2 having a LAN-WAN-LAN connection format are connected to the same segment (e.g., LAN-II), and a LAN-WAN-LAN setup are well known as configurations which are improved over those in FIGS. 52 and 53.
In this case, so long as the router Bxe2x80x2 of LAN-II functions regularly, even when the router B malfunctions the network can be connected to another segment via the router Bxe2x80x2. However, to do this, a switching function is required by which the xe2x80x9crouter Bxe2x80x9d and the xe2x80x9crouter Bxe2x80x2,xe2x80x9d as routers for communicating with other segments, can be set in the terminal DTE-b in the LAN-II segment, and by which the router Bxe2x80x2 can be employed when the router B does not respond.
A method has been proposed whereby two routers are mounted in a single segment, with one of them serving as a reserve for the other, and whereby the following operation is performed to ensure that communication with another segment is possible, even without the inclusion of the above described switching function (Japanese Laid-open Patent Publication Nos. Hei 7-154429, Hei 8-256173 and Hei 4-27239).
According to the technique described, for example, in Japanese Laid-open Patent Publication No. Hei 7-154429, the table information shown in FIG. 56 is prepared in the reserve router Bxe2x80x2. The tables are an address management information table (FIG. 56A) and a routing table (FIG. 56B)
In the address management table are entered a line type for each port of the reserve router Bxe2x80x2, and a port IP address and a MAC address both for normal operations and for operations when a fault occurs at the router B. Registered in the routing table are output ports for all of the destination addresses.
An explanation will be given while referring to the network in FIG. 55 for the outline of an operation, for which such table information is employed, performed by a currently employed router and a reserve (extra) router.
(1) First, the reserve router Bxe2x80x2 constantly monitors the currently employed router B in accordance with an ICMP (Internet Control Message Protocol) ECHO message (hereinafter referred to as a PING packet).
(2) When no response to the PING packet is transmitted by the current router B, operation of the reserve router Bxe2x80x2, using the same setup as that which is used for the current router B, is initiated to ensure uninterrupted communication with another segment.
However, only when the LAN-WAN-LAN connection format is employed does it appear to the terminal that the same setup is being used for the operation of the current router B and the reserve router Bxe2x80x2.
According to the techniques described in Japanese Unexamined Patent Publication Nos. Hei 8-256173 and Hei 4-27239, use of the reserve (extra) router Bxe2x80x2 is not initiated until the currently employed router B malfunctions, but in this case, since two routers are provided for a single segment, manufacturing costs are increased.
It is, therefore, one objective of the present invention to provide a configuration whereby, when a fault occurs at one of two or more routers in a network for the common performance of independent IP (Internet Protocol) communication, a different router (hereinafter referred to as a proxy router), which is set in advance to replace the malfunctioning router, can not only provide a normal communication function but also, for a subordinate segment serviced by the malfunctioning router, can continue to provide the same network environment as that available during normal operation with no adverse peripheral affect.
It is another objective of the present invention to provide a router network in which it is not necessary for two routers to be used in a specific segment and a terminal can assume that there is only one router in each segment, so that even when a fault occurs at a dedicated router for a specific segment it is ensured that communication will not be interrupted with any other segment.
It is an additional objective of the present invention to provide a router network which, regardless of the format used for a network, ensures that communication with another segment will be maintained, even though a fault may occur at a router.
To achieve the above objectives, the basic configuration according to the present invention is provided for a router network comprising a plurality of local area networks (LANs), furnished with routers for independent communication, whereby the plurality of local area networks communicate with each other using the Internet protocol (IP) or the Internet work packet protocol (IPX). A network environment for a subordinate segment serviced by a specific router is established for a different router, and when a fault occurs at the specific router, the different router is used as a proxy router to provide communication support for the subordinate segment of the specific router in accordance with the network environment which was set in advance.
When the recovery of the specific router from the fault is detected while the different router is acting as the proxy router, the different router releases the network environment which was set in advance for the subordinate segment of the specific router.
When the different router is being operated as a proxy router, a destination MAC (Media Access Control) address provided for an input frame is employed to determine the MAC address of a transmission source for a frame which is to be output.
In addition, when a frame is received from a port opposite a router connected to a dedicated line or to a public telephone line, while the different router is being operated as a proxy router, the MAC address of the transmission source is determined in accordance with the port at which the frame is input.
Furthermore, when a frame is received from a port opposite a router connected across an asynchronous transfer mode (ATM) network, while the different router is being operated as a proxy router, the MAC address of a transmission source for a frame to be output is determined in accordance with an input port and an input logical path (VPI/VCI: Virtual Path Identifier/Virtual Channel Identifier).
Further, when the different router is being operated as a proxy router, the different router takes the place of the specific router, which has malfunctioned, and transmits an RIP packet to the other routers.
Also, the specific router and the different router are connected to the same ATM network, and through an OAM (Operation, Administration and Maintenance) cell, the different router queries the ATM network setup for a logical path, with a port opposite the specific router where the fault has occurred, which is required in order for the different router to serve as a proxy router for the specific router.
Moreover, the specific router and the different router are connected to the same ATM network, and the different router employs an OAM (Operation, Administration and Maintenance) cell to transmit to the ATM network a path identifier for a router opposite the specific router where the fault has occurred, and queries the ATM network the connection of a logical path in accordance with the path identifier, in order for the different router to serve as a proxy router for the specific router.
Moreover, an ATM switch constituting the ATM network employs as a trigger the OAM (Operation, Administration and Maintenance) cell, which is transmitted by the router, to reset the logical path based on logical path setup information which was registered in advance.
In addition, the logical path is re-set by reading information from the OAM (Operation, Administration and Maintenance) cell transmitted by the router.
The other objectives and features of the present invention will become apparent during the course of the explanation for the following embodiment, which is given while referring to the accompanying drawings.